Sundials - World's Oldest Clocks

North American Sundial Society

Transits Time and Longitude

Here we showcase various natural and scientific phenomena related to the sun and solar alignments, and the quest for measuring time and longitude.

Perryville Eclipse SundialPerryville Eclipse Sundial

In Perryville, Missouri, Perry County unveilled a sundial  commemprating the coming August 21st total solar eclipse. Mike Mohundro, Photojournalis for Hearland News (KFVS Channel 12) interviewed Trish Erzfeld, Perry Count Heritage Tourism Director, who said "We just wanted something after the eclipse is over with that the community can be proud of and reflect back on."  Mohundro went on to write "many organizations worked on this project together including Earthworks, the [North] American Sundial Society, St. Louis Stone Artist Abraham Mohler, Perry County and more."

The sundial, shown in a KFVS video and in the photo at right, is a horizontal white milk glass sundial now mounted on a large marble pedestal (watch the dial video at 

On the pedestal are three plaques, one entitled "Time" explaining how to convert the sundial's solar time to civil time as told by watches and cellphones. "Not a lot of people know how to read a sundial," Erzfeld said. "It's a teaching tool as well as a historical marker here on out." The second plaque entitled "Eclipse" shows the date and time when the August 21st eclipse starts and stops as seen in Perryville said Don Snyder, local member of the North American Sundial Society.  The third plaque "Sundial" indicates who was involved in creating the dial.

Mohundro quotes Erzfeld saying "Education is been our main focus through this whole solar eclipse even... There's just so many things that play into the science of it and a sundial is one of those things that people can learn from."

A sundial that only tells time during an eclipse?  Back in 2012 Bill Gottesman designed a peculiar dial to tell time by observing the angle between the cusps of the sun during the May 2012 eclipse.  Bill Gottesman is back at it with a more sophisticated version assisted by programmer Dan Axtell.  This time Bill and Dan give you an animated version of the cusp line, as well as detailed information of the line angle during the eclipse.  

This is for anywhere in North America that can see the partial or total eclipse.  Just enter your latitude and longitude and let the software create you a personal solar eclipse sundial. PLEASE DO NOT OBSERVE THE SUN DIRECTLY WITHOUT AN APPROVED SOLAR FILTER... OR, MAKE A SIMPLE PINHOLE CAMERA FROM A CARDBOARD BOX.

To make your solar eclipse sundial, go to

The North American Sundial Society will meet in St. Louis for their annual meeting and to observe the Great American Solar Eclipse on August 21, 2017.  Cities and towns across the US are planning events and raising awareness of both the beauty and hazards of the solar eclipse. For the last two years St. Louis groups have delivered more than 100 programs to area schools, libraries, cities, parks and businesses to raise awareness of this historic event which has not happened in St. Louis since the year 1442. 

Remember, except for the minute or two of totality, looking directly at the sun will do serious eye damage.  Use sun-safe eyeglasses (certified safe for solar viewing) available from many source (see links below or Amazon, etc.). Read about the Great American Eclipse coming near you:

St. Louis, IL:

Other Cities:

The 2017 August 21st solar eclipse will be commemorated by the US Postal Service with a unique thermochromic ink Forever Stamps: the stamp shows the total Eclipse of the Sun with its corona blocked by a black disk of the moon.  However, using the body heat of your thumb or fingers the eclipse image will reveal an underlying image of the moon. The image reverts back to the eclipse once it cools. Fred Espenak, "Mr. Eclipse" a retired NASA astrophysicist, took the photograph of both the eclipse (from Jalu, Libya on March 29, 2006) and the full moon.

The USPS  states that June 20, 1:30 p.m. MT will be theFirst-Day-of-Issue ceremony, taking place at the Art Museum of the University of Wyoming (UW) in Laramie. The University is celebrating the summer solstice on June 20. Prior to the stamp issuance, visitors are encouraged to arrive at UW's Art Museum's Rotunda at 11:30 a.m. to witness a unique architectural feature at noon when a single beam of sunlight shines from down on a silver dollar embedded in the floor, marking noon on the summer solstice,

The Total Eclipse of the Sun Forever Stamps may be pre-ordered at in early June for delivery following the June 20 nationwide issuance.  The back of the stamp pane provides a map of the eclipse path and times it appears at cities across the US.

Back Panel of the Eclipse Stamp

Read more at: NASA Eclipse    and for observing tips

At the Grolier Club on the Upper East Side of Manhattan is a massive exhibit  On Time: The Quest for Precision curated by Bruce Bradley.  The exhibit presents the progress of timekeeping over six centuries through 86 rare books from the Linda Hall Library of Science, Engineering & Technology.

La pratique et demonstration des horloges solaires
1624 La pratique et demonstration des horloges solaires

Journalist Allison Meier of describes a number of books on display such as "German cartographer Sebastian Münster’s 1533 Horologiographia, the first book devoted to sundials, with woodcuts attributed to Hans Holbein the Younger."  As shown in her photo, "French engineer Salomon de Caus’s 1624  La pratique et demonstration des horloges solaires has embedded pop-ups to make the workings of its sundials easier to replicate."

The scope of "On Time" stretches from sundials, to water clocks, mechanical clocks and even a Pilkington & Gibbs Heliochronometer, ending with our latest atomic clocks.  The display flirts with the possible.  While Benjamin Franklin may have suggested using hourly time-telling canon in the 18th century, Athanasius Kircher proposed a fanciful firing sundial a century earlier in his 1646 Ars magna lucis et umbrae in decem libros digesta. His bowl-shaped sundial holds gunpowder at the hours that is ignited by the rays of the sun from a lens.  In turn the firing gunpowder triggers hammers to toll hourly bells. If one thinks about this for a moment, Kircher's proposal is as unrealistic as Franklin's.  The change in solar declination creates problems for proper placement of the gunpowder, let alone directing the ignition to trigger hammers.

Allison observes that "These manuscripts affirm the centuries of shared ideas that give our modern timekeeping devices their precision."  On Time: The Quest for Precision" continues through November 19, 2016.

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